• Title/Summary/Keyword: Crystal Size Distribution

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A Study on the Effect of Fluid Flow on the Microstructure of High Purity Al Ingot under Forced Flow (강제대류시 고순도 Al괴의 응고조직에 미치는 유동의 영향)

  • Kim, Kyoung-Min;Kim, Heon-Joo;Ha, Ki-Yun;Yoon, Eui-Pak
    • Journal of Korea Foundry Society
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    • v.13 no.6
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    • pp.540-546
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    • 1993
  • The effects of fluid flow on the purification of aluminum were studied. As the revolution rate(N) increased, the size of columnar grain decreased gradually. The concentration of solidified crystal was decreased with increasing distance from chill and revolution rate(N). Distribution boundary layer thickness(${\delta}$) was calculated from the solute distribution obtained in solid experimentally and by use of BPS equation. The value of ${\delta}$ changed from about $60{\mu}m$ at N value of 27rpm to about $15{\mu}m$ at N value of 1000rpm. From this result, high purification was obtained by decreasing the diffusion boundary layer under forced convection.

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Analysis of the Temperature Distribution at Micromachining Processes for Microaccelerometer Based on Tunneling Current Effect (턴널전류 효과를 이용한 미소가속도계의 마이크로머시닝 공정에서 온도분포 해석)

  • 김옥삼
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.9 no.5
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    • pp.105-111
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    • 2000
  • Micronization of sensor is a trend of the silicon sensor development with regard to a piezoresistive silicon pressure sensor, the size of the pressure sensor diaphragm have become smaller year by year, and a microaccelerometer with a size less than 200~300${\mu}{\textrm}{m}$ has been realized. Over the past four or five years, numerical modeling of microsensors and microstructures has gradually been developed as a field of microelectromechanical system(MEMS) design process. In this paper, we study some of the micromachining processes of single crystal silicon(SCS) for the microaccelerometer, and their subsequent processes which might affect thermal and mechanical loads. The finite element method(FEM) has been a standard numerical modeling technique extensively utilized in structural engineering discipline for component design of microaccelerometer. Temperature rise sufficiently low at the suspended beams. Instead, larger temperature gradient can be seen at the bottom of paddle part. The center of paddle part becomes about 5~2$0^{\circ}C$ higher than the corner of paddle and suspended beam edges.

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Synthesis and Analysis of Nanosized TiO2 Particles Using a Tube Furnace (튜브 전기로를 이용한 TiO2 나노입자의 합성 및 특성 분석)

  • 배귀남;현정은;이태규;정종수
    • Journal of Korean Society for Atmospheric Environment
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    • v.20 no.3
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    • pp.411-419
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    • 2004
  • Titania particles are widely used as a photocatalyst to treat various contaminants in air and water. Titania particles were formed by vapor-phase oxidation of titanium tetraisopropoxide (TTIP) in a tube furnace between 773 and 1,273 K. The effect of process variables such as furnace temperature, flow rate of carrier air, and flow rate of sheath air on powder size and phase characteristics was investigated using a scanning mobility particle sizer (SMPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The size distribution of synthesized titania particles was characterized with mode diameter and peak concentration. The mode diameter ranging from 20 to 80 nm decreased with increasing flow rates of sheath air and carrier air, and increased with increasing furnace temperature. The peak concentration increased with increasing flow rates of sheath air and carrier air The best synthetic condition for high production rate can be derived from the experimental data set represented by mode diameter and peak concentration. The crystal structure of synthesized titania particles was found to be anatase phase, ensuring high photocatalytic potential.

Synthesis of Manganese Hydrogen Phosphate Hydrate by Controlled Double-jet Precipitation (더블제트 침전법에 의한 제이인산망간염 수화물의 새로운 합성 방법)

  • Kim, Won-Seok;Kang, Yong;Kim, Yeong-Cheol
    • Applied Chemistry for Engineering
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    • v.19 no.1
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    • pp.66-72
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    • 2008
  • Manganese hydrogen phosphate hydrate, $MnHPO_4{\cdot}2.25H_2O$, is a major constituent of the pre-conditioning compositions for the manganese phosphate coating treatment over carbon steel substrate. This compound is conventionally produced by the synthesis in the aqueous solution process followed by the filtration and drying processes and a series of size reduction and classification processes in dry state. However, it is evident that the conventional process is neither environment-friendly nor cost-effective. In this work, a new process principle was examined based on the controlled double-jet precipitation technology to produce the manganese chemical product of fairly uniform particle size distribution in an aqueous solution media. The effects of stabilizing agents were comparatively studied by the scanning electron microscope analysis in a uniformity point of view of the resulting particle size. Polyvinylpyrrolidone and Gum Arabic were excellent in controlling the crystal growth step, resulting in fairly uniform size distributions of the particles from the controlled double-jet process.

Synthesis of Nanosized Cu/Zn Particles in the Base Oil Phase by Hydrothermal Method and Their Abrasion Resistance (기유 내에서 수열합성법에 의한 나노크기의 구리/아연 입자 합성 및 윤활 특성)

  • Kim, Young-Seok;Lee, Ju-Dong;Lee, Man-Sig
    • Journal of the Korean institute of surface engineering
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    • v.40 no.1
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    • pp.11-15
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    • 2007
  • Stable metallic Cu/Zn nanoparticles were prepared in the base oil phase by hydrothermal method. The physical properties, such as crystal structure, crystallite size and crystallinity according to synthesis conditions have been investigated by XRD, FT-IR and TEM. In addition, 4-ball test has been performed in order to investigate the frictional wear properties of prepared nanosized Cu/Zn particles. The peaks of the X-ray diffraction pattern indicate that the particle size was very small and crystallinity of Cu/Zn particles was good. The micrographs of TEM showed that nanosized Cu/Zn particles possessed a spherical morphology with a narrow size distribution. The crystallite size of the Cu/Zn particles synthesized in base oils was 23-30 nm. It was found that the antiwear capacity increases with increasing Cu/Zn concentration. When the concentration of Cu/Zn was 5.0 wt%, the wear scar diameters was 0.38 mm.

Establishment of Fundamental Process Conditions on Properties of Magnesium Alloy Thin Plates Fabricated by the Melt Drag Method (용융드래그방법으로 제작한 마그네슘합금 박판의 특성에 미치는 기본적인 공정조건 확립)

  • Han, Chang-Suk;Lee, Chan-Woo
    • Korean Journal of Materials Research
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    • v.32 no.7
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    • pp.326-331
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    • 2022
  • AZ31 magnesium alloy was used to manufacture a thin plate using a melt drag method. The effects of roll speed, molten metal temperature, and molten metal height, which are the basic factors of the melt drag method, on the surface shape, the thickness of the thin plate, Vickers hardness, and microstructure of the thin plate were investigated. It was possible to manufacture AZ31 magnesium alloy thin plate at the roll speed range of 1 to 90 m/min. The thickness of the thin plate, manufactured while changing only the roll speed, was about 1.8 to 8.8 mm. The shape of the solidified roll surface was affected by two conditions, the roll speed and the molten metal height, and the Vickers hardness of the manufactured magnesium alloy thin plate value ranged from Hv38~Hv60. The microstructure of the thin plate produced by this process was an equiaxed crystal and showed a uniform grain size distribution. The grain size was greatly affected by the contact state between the molten metal and the solidification roll, and the amount of reactive solids and liquids scraped at the same time as the thin plate. The average grain size of the thin plate fabricated in the range of these experimental conditions changed to about 50-300 ㎛.

Effects of Temperature and Saturation on the Crystal Morphology of Aragonite (CaCO3) and the Distribution Coefficient of Strontium: Study on the Properties of Strontium Incorporation into Aragonite with respect to the Crystal Growth Rate (온도와 포화도가 아라고나이트(CaCO3)의 결정형상과 스트론튬(Sr)의 분배계수에 미치는 영향: 결정성장속도에 따른 아라고나이트 내 스트론튬 병합 특성 고찰)

  • Lee, Seon Yong;Chang, Bongsu;Kang, Sue A;Seo, Jieun;Lee, Young Jae
    • Korean Journal of Mineralogy and Petrology
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    • v.34 no.2
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    • pp.133-146
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    • 2021
  • Aragonite is one of common polymorphs of calcium carbonate (CaCO3) and formed via biological or physical processes through precipitation in many different environments including marine ecosystems. It is noted that aragonite formation and growth as well as the substitution of trace elements such as strontium (Sr) in the aragonite structure would be dependant on several key parameters such as concentrations of chemical species and temperature. In this study, properties of the incorporation of Sr into aragonite were investigated over a wide range of various saturation conditions and temperatures similar to the marine ecosystem. All pure aragonite samples were inorganically synthesized through a constant-addition method with varying concentrations of the reactive species ([Ca]=[CO3] 0.01-1 M), injection rates of the reaction solution (0.085-17 mL/min), and solution temperatures (5-40 ℃). Pure aragonite was also formed even under the Sr incorporation conditions (0.02-0.5 M, 15-40 ℃). When temperature and saturation index (SI) with respect to aragonite increased, the crystallinity and the crystal size of aragonite increased indicating the growth of aragonite crystal. However, it was difficult to interpret the crystal growth rate because the crystal growth rate calculated using BET-specific surface area was significantly influenced by the crystal morphology. The distribution coefficient of Sr (KSr) into aragonite decreased from 2.37 to 1.57 with increasing concentrations of species (Ca2+ and CO32-) at a range of 0.02-0.5 M. Similarly, it was also found that KSr decreased 1.90 to 1.54 at a range of 15-40 ℃. All KSr values are greater than 1, and the inverse correlation between the KSr and the crystal growth rate indicate that Sr incorporation into aragonite is in a compatible relationship.

Polymorphism of Calcium Carbonate Crystal by Addition of Various Amino (다양한 아미노산의 첨가에 의한 탄산칼슘 결정의 Polymorphism)

  • Kim, Jin-Ho;Kim, Jong Min;Kim, Woo Sik;Kim, In Ho
    • Korean Chemical Engineering Research
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    • v.47 no.2
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    • pp.213-219
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    • 2009
  • Crystallization experiments were performed by addition of various amino acids into biomineralization mixture of calcium carbonate. Liquid-liquid reaction of calcium carbonate was investigated by mixing calcium chloride, sodium carbonate and additives such as silk fibroin, asparagine, aspartic acid, glutamic acid and glycine. Also, the effects of reaction time, pH and solution concentration were observed. Analysis of crystals was done by FE-SEM, XRD, FT-IR equipments. FE-SEM was used in order to analyze morphology and crystal size. XRD was used to measure peak intensities and presence of $CaCO_3$ crystal. Two kinds of crystals were confirmed by FT-IR spectrum. Crystal distribution with reaction time was identified with measured peak areas of XRD and FT-IR data.

Reactive Dye(RB-8, RB-49, RR-218) in Crystallization and Characteristic of Population Density (반응성 염료(RB-8, RB-49, RR-218)의 결정화 및 입도분포 특성)

  • Han, Hyunkak;Lee, Jonghoon;In, Daeyoung
    • Korean Chemical Engineering Research
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    • v.50 no.2
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    • pp.198-203
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    • 2012
  • Salting-out technique was adopted to crystallize dye crystals from dye solution. In this research solubility of dye solution and crystallization kinetics of Reactive dye (RB-8, RB-49, RR-218) was investigated. The empirical expressions of salting-out crystallization kinetics for Reactive dye (RB-8, RB-49, RR-218) in continuous MSMPR crystallizer was RB-8 in crystal growth kinetics $G=7.1{\times}10^{-4}{\Delta}C^{0.67}$ and nucleation kinetics $B^0=3.1{\times}10^{15}{\Delta}C[1.2{\times}10^{-8}+{\Delta}C^{0.7}M_T{^2}]$, RB-49 in crystal growth kinetics $G=5.2{\times}10^{-4}{\Delta}C^{0.3441}$ and nucleation kinetics $B^0=7.2{\times}10^{15}{\Delta}C[3.3{\times}10^{-8}+({\Delta}C)^{0.7}M_T{^2}]$, RR-218 in crystal growth kinetics $G=4.4{\times}10^{-4}{\Delta}C^{0.2361}$ and nucleation kinetics $B^0=6.3{\times}10^{15}{\Delta}C[7.9{\times}10^{-8}+({\Delta}C)^{0.7}M_T{^2}]$. Also, comparison of calculated crystal size distribution applying to characteristic curve method with experimental crystal size showed good agreement.

Fabrication of $TiN_x$ by planetary milling (Planetary milling에 의한 $TiN_x$의 제조)

  • Kim, Sung-Jin;Kim, Dong-Sik;Rahno, Khamidova;Park, Sung-Bum;Gwon, Won-Il;Kim, Moon-Hyup;Woo, Heung-Sik;Ahn, Joong-Ho
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.15 no.3
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    • pp.104-107
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    • 2005
  • [ $TiN_x$ ] powder have been fabrication by making of reaction between titanium powder and $Si_3N_4$ bowl during a planetary milling. Milling times were maintained for 1 hour, 5 hours, and 10 hours, respectively. The XRD result showed existence of non-stoichiometric compound of $TiN_{0.26}$ after 5 hours milling and coexistence of TiN with $TiN_{0.26}$ after 10 hours milling. Particle size distribution was investigated by particle size analyzer and microstructure was analyzed by FE-SEM. The size of titanium was decreased with increasing the milling time and the mean size of $TiN_x$ after 10 hours milling was increased by 200 nm.